The present invention relates to an apparatus and a method for direct injection moulding of a plastics material opening device to a hole provided on a sheet of packaging material. The term xe2x80x9copening devicexe2x80x9d as used herein, refers mainly to opening devices used for pouring liquid contents from a container, but also includes opening devices which may be used for filling a container.
Opening devices of different types provided on a packaging container formed by packaging sheet material and adapted for containing substances such as foodstuffs, and in particular for containing liquid beverages such as juices, water, milk, wine, etc. are known.
One such opening device includes a perforation on a wall part of the packaging container and a plastics material lid device attached to the wall part and covering the perforation in a closed state. The lid device includes a circumferential base attached to the wall part, for example by means of adhesives, circumferentially surrounding the perforation, and a lid element hinged to the base. Once the lid element is opened, the perforation may be engaged and forced open so that the contents inside the packaging container may be dispensed therefrom.
Another known opening device includes an opening provided on a wall part of the packaging container and a plastics material lid device similar to the one described above attached to the wall part and covering the opening in a closed state. A sealing element such as an aluminium pull tab is connected to the wall part so as to cover the opening, and once the lid element has been opened, the sealing element may be removed to expose the opening for dispensing the contents of the packaging container.
Methods for providing the above opening devices on the packaging containers may include feeding a continuous web of packaging material to a first station at which the perforation or opening is provided on the web, and to a second station at which the lid element is attached to the web for covering the perforation or opening. The aluminium pull tab, if provided i.e. for covering the opening, is attached in an intermediate step. After the opening devices are provided on the web, packaging containers from the web are formed, filled with product, and sealed, such that the opening devices are arranged on the finished container packagings for easy access.
One example of a machine for forming, filling, and sealing packaging containers is the TB8 filling machine, manufactured by Tetra Brik Packaging Systems of Modena, Italy.
As an alternative to the above opening devices, in which an already formed plastics material lid device is applied to the sheet, U.S. Pat. No. 4,725,213 (the disclosure of which is incorporated herein by reference) discloses a plastics material opening device which is injection moulded directly onto the sheet of packaging material. In particular, a pair of mould tools are moved into arrangement about a prestamped hole in the sheet, and heated thermoplastics material is injected through an injection passage defined between one of the mould tools and one surface of the sheet and extending along such surface of the sheet in order to form the opening device at the prestamped hole.
Although the method and apparatus for providing this latter type of opening device may be completely valid, there exists in the field of thermoplastics material injected opening devices the need for further improvements.
The injection passage in U.S. Pat. No. 4,725,213 extends from the injector head for a significant distance along one surface of the sheet to one end of the mould cavity for forming the opening device, so as to create a number of disadvantageous effects. Since the injection passage enters the mould cavity at one end, the complete filling of the mould cavity with heated thermoplastics material is rendered difficult and inefficient particularly at the portion of the mould cavity arranged distally from the injection passage. Moreover, if the injection passage extending along one surface of the sheet is excessively long, the filling of the mould cavity is rendered even more difficult and inefficient, and therefore the apparatus and method are limited to moulding opening devices arranged substantially only near the edge of the sheet at which the injection head is positioned. Additionally, a strip of plastics material is formed in the injection passage, and further steps must be made to eliminate such strip, which is additionally inefficient and which creates the possibility of damaging the opening device from which such strip must be removed. Further complications arise from subjecting the surface of the sheet of packaging material, which generally has a very low stiffness and resistance, to thermoplastics material at elevated pressures and temperatures injected into the injection passage.
The above described difficulties in completely filling the mould cavity may lead to a situation in which plastics material will not flow to all parts of the mould cavity and as a result, the edge of the opening may not be sufficiently to sealed by plastics material of the opening device. Generally, the packaging sheet material is formed of several layers including an inner paper layer and two outer synthetic plastics material coating layers, one of which is destined to form a product contact surface. Other possible layers such as printing ink layers, laminating layers and aluminium foil layers may be interposed between the paper layer and the outer coating layers. When the opening in the packaging sheet material is stamped, the internal layers of the packaging sheet are exposed at the edge of the opening, and unless such edge is adequately sealed by the injected thermoplastics material opening device, the packaged product may come into contact with the internal layers of the packaging sheet material possibly causing damage thereto. Moreover, the overall efficiency of the apparatus and method is compromised when the time needed to inject the heated thermoplastics material for each mould operation is increased so as to assure an adequate filling of the mould cavity.
The mould tools in U.S. Pat. No. 4,725,213 consist of a pair of mould tools which are both movable in opening and closing directions which extend perpendicularly to the extension of the sheet. Such a configuration substantially limits the flexibility of the device in forming opening devices with different shapes, since the mould tools must not encounter any portions of the opening device which protrude in a direction perpendicular to the direction of movement of the mould tools. The injection moulded opening device of U.S. Pat. No. 4,725,213 indeed includes a pull tab which extends in a direction perpendicular to the sheet, for a long extension sufficient to be gripped by a user. Such an extensively protruding pull tab is disadvantageous with regard to storing and shipping packaging containers including an opening device of this type.
It is furthermore desirous to have opening devices with base portions connected to the sheet hole and lid portions positioned in planes which are slightly raised with respect to the base portions and the packaging sheet. These lid portions have an edge or lip which extends parallel to the extension of the packaging sheet, so that they may be gripped and opened by a user. The apparatus of U.S. Pat. No. 4,725,213 is incapable of forming opening devices of this type due to the opening movement of the mould tools.
What is needed is an apparatus and method for injection moulding a thermoplastics material opening device onto a packaging material sheet which allows to assure that the opening device is moulded in a most effective and efficient manner possible.
In accordance with one preferred aspect of the invention, there is provided in a packaging machine for forming package containers from a driven web of packaging sheet material, an opening device moulding station for moulding opening devices on to the web at respective holes provided in the web, which opening device moulding station includes first and second mould tools releasably arrangeable in closed positions so as to form a mould cavity for accommodating the hole edge of the web. An injection passage for injecting heated thermoplastics material into the mould cavity extends in at least one of the first and second mould tools such that the thermoplastics material is injected directly into the mould cavity at an injection point of the mould cavity which is located distally from the hole edge.
By having the injection point arranged distally from the hole edge, the heated thermoplastics material advantageously enters the mould cavity at a position which permits the filling of the mould cavity to be carried out in an effective and efficient manner. The heated plastics material will flow from the injection point smoothly and evenly initially distally from the hole edge and successively fill the mould cavity so that the heated plastics material makes contact with the hole edge at the end of the injection step. The times required for each injection step are therefore minimised in order to increase the efficiency of the opening device moulding operation.
According to a most preferred aspect of the invention, the injection point is arranged at a lid forming portion of the mould cavity, in a substantially central position with respect to a base forming portion of the mould cavity, and the injection passage extends in one of the mould tools in a direction which is substantially perpendicular to the extension of the lid forming portion of the mould cavity. Such a configuration allows to fully maximise the efficiency of material flow from the injection point in a symmetrical and even manner initially distally from the hole edge and successively to fill the base forming portion of the mould cavity. Such configuration also allows to fully avoid subjecting surfaces of the web to the flow of heated thermoplastics material.
In accordance with another preferred aspect of the invention, there is provided an opening device moulding apparatus for moulding plastics material opening devices on to a sheet at respective holes provided in the sheet, which opening device moulding apparatus includes first and second mould tools releasably arrangeable in closed positions so as to form a mould cavity for accommodating the hole edge of the sheet, a drive mechanism for selectively moving the first mould tool and said second mould tool between the open and closed positions, and at least one of the first and second mould tools includes a pair of half mould tools. The drive mechanism includes a supporting structure for supporting the half mould tools such that in the open position the half mould tools are mutually spaced from each other in an extension plane extending substantially parallel to the plane of extension of the sheet and such that in the closed position the half mould tools are mutually arranged in contact with each other. The drive mechanism further includes a driver for moving the half mould tools simultaneously from the open position to the closed position and vice versa such that the direction of movement of each of the half mould tools between the open and closed positions comprises a directional component extending parallel to the sheet extension plane and a directional component extending perpendicularly to the sheet extension plane.
With such a configuration of the drive mechanism, it is advantageously possible to effectively directly mould opening devices of many various shapes which may include, in particular, portions which protrude and extend in a plane which is parallel to the extension plane of the sheet. Moreover, the particular configuration of the drive mechanism is such that the half mould tools mutually arrive and make contact together at the closed position with a delicate approach so as to provide for minimum wear of the half mould tools. According to a most preferred embodiment, the drive mechanism is configured such that the direction of movement of each of the half mould tools between the open and closed positions tangentially follows a circular path, thereby for minimising the space requirements of the opening device moulding apparatus and for minimising wear on the half mould tools.
In accordance with yet another aspect of the invention, there is provided an opening device moulding apparatus for injection moulding plastics material opening devices at holes in a packaging material sheet, including first and second mould tools arrangeable in open and closed positions respectively spaced apart from and engaging the sheet, wherein in the closed position the sheet extends in a plane which is distally spaced from the plane of extension of the sheet in the open position. When the sheet is spaced from its normal extension by the mould tools in the closed position, it is put under an added tension which advantageously facilitates the release of the sheet and moulded opening device from the mould tools as such mould tools move away from the closed position to the open position.
The technical characteristics and advantages of the present invention will become apparent to those skilled in the art from the following detailed description of some preferred embodiments thereof, described and illustrated in the accompanying drawings only by way of non-limitative example, wherein like reference numerals indicate like parts.